The ornamental design for a hairextensiontool, as shown and described.
1. Hair extension tool
1.1 : Perspective
1.2 : Front
1.3 : Back
1.4 : Left
1.5 : Right
1.6 : Top
1.7 : Bottom
This article is a tool used for extending hair by attaching, for example, synthetic hair to a person's natural hair; reproduction 1.1 is a perspective view; reproduction 1.2 is a front view; reproduction 1.3 is a back view; reproduction 1.4 is a left view; reproduction 1.5 is a right view; reproduction 1.6 is a top view; and, reproduction 1.7 is a bottom view; the dashed broken lines in the reproductions represent portions of the hair extension tool that form no part of the claimed design; the dot-dash broken lines shown in the reproductions represent unclaimed boundaries and form no part of the claimed design.